This document describes the basic NFC tasks you perform in Android. It explains how to send and
receive NFC data in the form of NDEF messages and describes the Android framework APIs that support
these features. For more advanced topics, including a discussion of working with non-NDEF data,
see Advanced NFC.

There are two major uses cases when working with NDEF data and Android:

Reading NDEF data from an NFC tag is handled with the tag dispatch
system, which analyzes discovered NFC tags, appropriately categorizes the data, and starts
an application that is interested in the categorized data. An application that wants to handle the
scanned NFC tag can declare an intent filter and
request to handle the data.

The Android Beam™ feature allows a device to push an NDEF message onto
another device by physically tapping the devices together. This interaction provides an easier way
to send data than other wireless technologies like Bluetooth, because with NFC, no manual device
discovery or pairing is required. The connection is automatically started when two devices come
into range. Android Beam is available through a set of NFC APIs, so any application can transmit
information between devices. For example, the Contacts, Browser, and YouTube applications use
Android Beam to share contacts, web pages, and videos with other devices.

The Tag Dispatch System

Android-powered devices are usually looking for NFC tags when the screen
is unlocked, unless NFC is disabled in the device's Settings menu.
When an Android-powered device discovers an NFC tag, the desired behavior
is to have the most appropriate activity handle the intent without asking the user what application
to use. Because devices scan NFC tags at a very short range, it is likely that making users manually
select an activity would force them to move the device away from the tag and break the connection.
You should develop your activity to only handle the NFC tags that your activity cares about to
prevent the Activity Chooser from appearing.

To help you with this goal, Android provides a special tag dispatch system that analyzes scanned
NFC tags, parses them, and tries to locate applications that are interested in the scanned data. It
does this by:

Parsing the NFC tag and figuring out the MIME type or a URI that identifies the data payload
in the tag.

How NFC tags are mapped to MIME types and URIs

Before you begin writing your NFC applications, it is important to understand the different
types of NFC tags, how the tag dispatch system parses NFC tags, and the special work that the tag
dispatch system does when it detects an NDEF message. NFC tags come in a
wide array of technologies and can also have data written to them in many different ways.
Android has the most support for the NDEF standard, which is defined by the NFC Forum.

NDEF data is encapsulated inside a message (NdefMessage) that contains one
or more records (NdefRecord). Each NDEF record must be well-formed according to
the specification of the type of record that you want to create. Android
also supports other types of tags that do not contain NDEF data, which you can work with by using
the classes in the android.nfc.tech package. To learn more
about these technologies, see the Advanced NFC topic. Working with these other types of tags involves
writing your own protocol stack to communicate with the tags, so we recommend using NDEF when
possible for ease of development and maximum support for Android-powered devices.

Now that you have some background in NFC tags, the following sections describe in more detail how
Android handles NDEF formatted tags. When an Android-powered device scans an NFC tag containing NDEF
formatted data, it parses the message and tries to figure out the data's MIME type or identifying
URI. To do this, the system reads the first NdefRecord inside the NdefMessage to determine how to interpret the entire NDEF message (an NDEF message can
have multiple NDEF records). In a well-formed NDEF message, the first NdefRecord
contains the following fields:

3-bit TNF (Type Name Format)

Indicates how to interpret the variable length type field. Valid values are described in
described in Table 1.

Variable length type

Describes the type of the record. If using TNF_WELL_KNOWN, use
this field to specify the Record Type Definition (RTD). Valid RTD values are described in Table 2.

Variable length ID

A unique identifier for the record. This field is not used often, but
if you need to uniquely identify a tag, you can create an ID for it.

Variable length payload

The actual data payload that you want to read or write. An NDEF
message can contain multiple NDEF records, so don't assume the full payload is in the first NDEF
record of the NDEF message.

The tag dispatch system uses the TNF and type fields to try to map a MIME type or URI to the
NDEF message. If successful, it encapsulates that information inside of a ACTION_NDEF_DISCOVERED intent along with the actual payload. However, there
are cases when the tag dispatch system cannot determine the type of data based on the first NDEF
record. This happens when the NDEF data cannot be mapped to a MIME type or URI, or when the
NFC tag does not contain NDEF data to begin with. In such cases, a Tag object that has information about the tag's technologies and the payload are
encapsulated inside of a ACTION_TECH_DISCOVERED intent instead.

Table 1. describes how the tag dispatch system maps TNF and type
fields to MIME types or URIs. It also describes which TNFs cannot be mapped to a MIME type or URI.
In these cases, the tag dispatch system falls back to
ACTION_TECH_DISCOVERED.

For example, if the tag dispatch system encounters a record of type TNF_ABSOLUTE_URI, it maps the variable length type field of that record
into a URI. The tag dispatch system encapsulates that URI in the data field of an ACTION_NDEF_DISCOVERED intent along with other information about the tag,
such as the payload. On the other hand, if it encounters a record of type TNF_UNKNOWN, it creates an intent that encapsulates the tag's technologies
instead.

URI based on the URN in the type field. The URN is encoded into the NDEF type field in
a shortened form: <domain_name>:<service_name>.
Android maps this to a URI in the form:
vnd.android.nfc://ext/<domain_name>:<service_name>.

How NFC Tags are Dispatched to Applications

When the tag dispatch system is done creating an intent that encapsulates the NFC tag and its
identifying information, it sends the intent to an interested application that
filters for the intent. If more than one application can handle the intent, the Activity Chooser
is presented so the user can select the Activity. The tag dispatch system defines three intents,
which are listed in order of highest to lowest priority:

ACTION_NDEF_DISCOVERED: This intent is used to start an
Activity when a tag that contains an NDEF payload is scanned and is of a recognized type. This is
the highest priority intent, and the tag dispatch system tries to start an Activity with this
intent before any other intent, whenever possible.

ACTION_TECH_DISCOVERED: If no activities register to
handle the ACTION_NDEF_DISCOVERED
intent, the tag dispatch system tries to start an application with this intent. This
intent is also directly started (without starting ACTION_NDEF_DISCOVERED first) if the tag that is scanned
contains NDEF data that cannot be mapped to a MIME type or URI, or if the tag does not contain NDEF
data but is of a known tag technology.

If no activities filter for that intent, try to start an Activity with the next
lowest priority intent (either ACTION_TECH_DISCOVERED or ACTION_TAG_DISCOVERED) until an application filters for the
intent or until the tag dispatch system tries all possible intents.

If no applications filter for any of the intents, do nothing.

Figure 1. Tag Dispatch System

Whenever possible, work with NDEF messages and the ACTION_NDEF_DISCOVERED intent, because it is the most specific out of
the three. This intent allows you to start your application at a more appropriate time than the
other two intents, giving the user a better experience.

Requesting NFC Access in the Android Manifest

Before you can access a device's NFC hardware and properly handle NFC intents, declare these
items in your AndroidManifest.xml file:

The NFC <uses-permission> element to access the NFC hardware:

<uses-permission android:name="android.permission.NFC" />

The minimum SDK version that your application can support. API level 9 only supports
limited tag dispatch via ACTION_TAG_DISCOVERED, and only gives
access to NDEF messages via the EXTRA_NDEF_MESSAGES extra. No
other tag properties or I/O operations are accessible. API level 10
includes comprehensive reader/writer support as well as foreground NDEF pushing, and API level
14 provides an easier way to push NDEF messages to other devices with Android Beam and extra
convenience methods to create NDEF records.

<uses-sdk android:minSdkVersion="10"/>

The uses-feature element so that your application shows up in Google Play
only for devices that have NFC hardware:

If your application uses NFC functionality, but that functionality is not crucial to your
application, you can omit the uses-feature element and check for NFC avalailbility at
runtime by checking to see if getDefaultAdapter()
is null.

Because NFC tag deployments vary and are many times not under your control, this is not always
possible, which is why you can fallback to the other two intents when necessary. When you have
control over the types of tags and data written, it is recommended that you use NDEF to format your
tags. The following sections describe how to filter for each type of intent.

ACTION_NDEF_DISCOVERED

To filter for ACTION_NDEF_DISCOVERED intents, declare the
intent filter along with the type of data that you want to filter for. The
following example filters for ACTION_NDEF_DISCOVERED
intents with a MIME type of text/plain:

ACTION_TECH_DISCOVERED

If your activity filters for the ACTION_TECH_DISCOVERED intent,
you must create an XML resource file that specifies the technologies that your activity supports
within a tech-list set. Your activity is
considered a match if a tech-list set is a subset of the technologies that are
supported by the tag, which you can obtain by calling getTechList().

For example, if the tag that is scanned supports MifareClassic, NdefFormatable, and NfcA, your
tech-list set must specify all three, two, or one of the technologies (and nothing
else) in order for your activity to be matched.

The following sample defines all of the technologies. You can remove the ones that you do not
need. Save this file (you can name it anything you wish) in the
<project-root>/res/xml folder.

You can also specify multiple tech-list sets. Each of the tech-list
sets is considered independently, and your activity is considered a match if any single
tech-list set is a subset of the technologies that are returned by getTechList(). This provides AND and OR
semantics for matching technologies. The following example matches tags that can support the
NfcA and Ndef technologies or can support the NfcB and Ndef technologies:

To obtain these extras, check to see if your activity was launched with one of
the NFC intents to ensure that a tag was scanned, and then obtain the extras out of the
intent. The following example checks for the ACTION_NDEF_DISCOVERED
intent and gets the NDEF messages from an intent extra.

Alternatively, you can obtain a Tag object from the intent, which will
contain the payload and allow you to enumerate the tag's technologies:

Tag tag = intent.getParcelableExtra(NfcAdapter.EXTRA_TAG);

Creating Common Types of NDEF Records

This section describes how to create common types of NDEF records to help you when writing to
NFC tags or sending data with Android Beam. Starting with Android 4.0 (API level 14), the
createUri() method is available to help you create
URI records automatically. Starting in Android 4.1 (API level 16),
createExternal()
and createMime() are available to help you create
MIME and external type NDEF records. Use these helper methods whenever possible to avoid mistakes
when manually creating NDEF records.

This section also describes how to create the corresponding
intent filter for the record. All of these NDEF record examples should be in the first NDEF
record of the NDEF message that you are writing to a tag or beaming.

Use TNF_EXTERNAL_TYPE for more generic NFC tag deployments to better support both
Android-powered and non-Android-powered devices.

Note: URNs for TNF_EXTERNAL_TYPE have a canonical format of:
urn:nfc:ext:example.com:externalType, however the NFC Forum RTD specification
declares that the urn:nfc:ext: portion of the URN must be ommitted from the
NDEF record. So all you need to provide is the domain (example.com in the example)
and type (externalType in the example) separated by a colon.
When dispatching TNF_EXTERNAL_TYPE, Android converts the urn:nfc:ext:example.com:externalType
URN to a vnd.android.nfc://ext/example.com:externalType URI, which is what the
intent filter in the example declares.

Android Application Records

Introduced in Android 4.0 (API level 14), an Android Application Record (AAR) provides a stronger
certainty that your application is started when an NFC tag is scanned. An AAR has the package name
of an application embedded inside an NDEF record. You can add an AAR to any NDEF record of your NDEF
message, because Android searches the entire NDEF message for AARs. If it finds an AAR, it starts
the application based on the package name inside the AAR. If the application is not present on the
device, Google Play is launched to download the application.

AARs are useful if you want to prevent other applications from filtering for the same intent and
potentially handling specific tags that you have deployed. AARs are only supported at the
application level, because of the package name constraint, and not at the Activity level as with
intent filtering. If you want to handle an intent at the Activity level, use intent filters.

If a tag contains an AAR, the tag dispatch system dispatches in the following manner:

Try to start an Activity using an intent filter as normal. If the Activity that matches
the intent also matches the AAR, start the Activity.

If the Activity that filters for the intent does not match the
AAR, if multiple Activities can handle the intent, or if no Activity handles the intent, start the
application specified by the AAR.

If no application can start with the AAR, go to Google Play to download the
application based on the AAR.

Note: You can override AARs and the intent dispatch system with the
foreground
dispatch system, which allows a foreground activity to have priority when an NFC tag is
discovered. With this method, the activity must be in the foreground to override AARs and the
intent dispatch system.

If you still want to filter for scanned tags that do not contain an AAR, you can declare
intent filters as normal. This is useful if your application is interested in other tags
that do not contain an AAR. For example, maybe you want to guarantee that your application handles
proprietary tags that you deploy as well as general tags deployed by third parties. Keep in mind
that AARs are specific to Android 4.0 devices or later, so when deploying tags, you most likely want
to use a combination of AARs and MIME types/URIs to support the widest range of devices. In
addition, when you deploy NFC tags, think about how you want to write your NFC tags to enable
support for the most devices (Android-powered and other devices). You can do this by
defining a relatively unique MIME type or URI to make it easier for applications to distinguish.

Android provides a simple API to create an AAR,
createApplicationRecord(). All you need to
do is embed the AAR anywhere in your NdefMessage. You do not want
to use the first record of your NdefMessage, unless the AAR is the only
record in the NdefMessage. This is because the Android
system checks the first record of an NdefMessage to determine the MIME type or
URI of the tag, which is used to create an intent for applications to filter. The following code
shows you how to create an AAR:

Beaming NDEF Messages to Other Devices

Android Beam allows simple peer-to-peer data exchange between two Android-powered devices. The
application that wants to beam data to another device must be in the foreground and the device
receiving the data must not be locked. When the beaming device comes in close enough contact with a
receiving device, the beaming device displays the "Touch to Beam" UI. The user can then choose
whether or not to beam the message to the receiving device.

Note: Foreground NDEF pushing was available at API level 10,
which provides similar functionality to Android Beam. These APIs have since been deprecated, but
are available to support older devices. See enableForegroundNdefPush() for more information.

You can enable Android Beam for your application by calling one of the two methods:

setNdefPushMessage(): Accepts an
NdefMessage to set as the message to beam. Automatically beams the message
when two devices are in close enough proximity.

The activity that is beaming the data must be in the foreground. Both devices must have
their screens unlocked.

You must encapsulate the data that you are beaming in an NdefMessage
object.

The NFC device that is receiving the beamed data must support the
com.android.npp NDEF push protocol or NFC Forum's SNEP (Simple NDEF Exchange
Protocol). The com.android.npp protocol is required for devices on API level 9 (Android
2.3) to API level 13 (Android 3.2). com.android.npp and SNEP are both required on
API level 14 (Android 4.0) and later.

Note: If your activity enables Android Beam and is
in the foreground, the standard intent dispatch system is disabled. However, if your activity also
enables
foreground dispatching, then it can still scan tags that match the intent filters set in the
foreground dispatching.

In general, you normally use setNdefPushMessage() if your Activity only needs to
push the same NDEF message at all times, when two devices are in range to communicate. You use
setNdefPushMessageCallback when your
application cares about the current context of the application and wants to push an NDEF message
depending on what the user is doing in your application.

Note that this code comments out an AAR, which you can remove. If you enable the AAR, the
application specified in the AAR always receives the Android Beam message. If the application is not
present, Google Play is started to download the application. Therefore, the following intent
filter is not technically necessary for Android 4.0 devices or later if the AAR is used:

With this intent filter, the com.example.android.beam application now can be started
when it scans an NFC tag or receives an Android Beam with an AAR of
type com.example.android.beam, or when an NDEF formatted message contains a MIME record
of type application/vnd.com.example.android.beam.

Even though AARs guarantee an application is started or downloaded, intent filters are
recommended, because they let you start an Activity of your choice in your
application instead of always starting the main Activity within the package specified by an AAR.
AARs do not have Activity level granularity. Also, because some Android-powered devices do not
support AARs, you should also embed identifying information in the first NDEF record of your NDEF
messages and filter for that as well, just in case. See Creating Common
Types of NDEF records for more information on how to create records.